The present invention relates to an auto-focus apparatus and control method for the same, and more particularly to an auto-focus apparatus and control method for the same used in a digital camera or a digital video camera.
A digital camera with various functions incorporated therein has become widespread in recent years. For example, a digital camera in which pixel number can be changed while recording has appeared in the market as well. This camera represents the needs of the user that sometimes they want to record the image at a higher quality and sometimes they want to record the image at a normal or lower quality. Namely, when an image to be recorded does not require high quality, a number of recording pixels is reduced while recording. Thus, the size of the file in which the image is recorded can be made smaller. The size of the file in which the image is recorded is becoming larger in association with the present trend of increase in the number of pixels in a CCD.
In addition, high-resolution AF control is demanded even under the conditions of the same focal length and the same CCD size in association with the present trend of increase in the number of pixels in a CCD.
In a digital camera which samples a AF evaluated value while driving a focus lens and detects a focus position, it is required to make smaller the interval of sampling of the AF evaluated value in order to provide AF control with high precision in a CCD having a large number of pixels therein. However, if the sampling interval is made smaller, a longer time is disadvantageously required for focusing.
It is an object of the present invention to provide, for the purpose of solving the problems described above, an auto-focus apparatus and control method for the same enabling high-precision focusing within a short period of time even when a CCD with a large number of pixels is used.
The auto-focus apparatus of the present invention comprises an image pickup device for converting light from an object through a focus lens system to electric signals and outputting the signals as image data; an A/D converting unit for A/D-converting the image data to obtain digital image signals; an AF evaluating unit for outputting an AF evaluated value obtained by integrating high-frequency components of brightness data for the digital image data; a sampling unit for sampling the AF evaluated value obtained by the AF evaluating unit while driving a position of the focus lens system; a recording pixel number setting unit for setting a number of recording pixels of the image pickup device for recording an image; and a focus driving unit for determining a focus according to a result of sampling of the AF evaluated value by the sampling unit and driving the focus lens system to the focus position; wherein amount of shift of the focus lens system for each sampling when sampling the AF evaluated value is changed according to a number of recording pixels set by the recording pixel number setting unit. Thus, the amount of shift of the focus lens system for each sampling when sampling the AF evaluated value can be changed according to a number of recording pixels set by the recording pixel number setting unit.
The auto-focus apparatus of the present invention comprises an image pickup device for converting light from an object through a focus lens system to electric signals and outputting the signals as image data; an A/D converting unit for A/D-converting the image data to obtain digital image signals: an AF evaluating unit for outputting an AF evaluated value obtained by integrating high-frequency components of brightness data for the digital image data; a sampling unit for sampling the AF evaluated value obtained by the AF evaluating unit while driving a position of the focus lens system; a recording pixel number setting unit for setting a number of recording pixels of the image pickup device for recording an image; and a focus driving unit for determining a focus according to a result of sampling of the AF evaluated value by the sampling unit and driving the focus lens system to the focus position: wherein during a first auto-focus operation, amount of shift of the focus lens system for sampling the AF evaluated value is set to a maximum and a substantial focus position is calculated; and during second auto-focus operation and thereafter, amount of shift of the focus lens system for sampling the AF evaluated value is set at a position closer to the substantial position to a minimum and the final focus position is obtained; and number of times the auto-focus operations are performed is changed according to the number of recording pixels set by the recording pixel number setting unit. Thus, a substantial focus position is obtained first and then a precise focus position is obtained from this substantial position.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.